The present invention relates to a magnetron which is an electron tube used for generating microwaves, and processing equipment employing the magnetron.
A magnetron can generate microwave power efficiently, and therefore is widely used in radar applications, medical applications, cooking appliances such as a microwave oven, semiconductor device manufacturing equipment, and other microwave applications.
FIG. 16 is a cross-sectional view of an essential part of an example of a conventional magnetron. In FIG. 16, reference numeral 1 denotes a filament serving as a thermionic electron source, 2 are plural anode vanes, 3 is an anode cylinder, 4 and 4a are annular permanent magnets, 5 and 5a are shallow-dish-shaped pole pieces, 6 and 6a are yokes, 7 is an antenna lead, 8 is an antenna, 9 is an exhaust tube, 10 is an antenna cover, 11 is an insulator, 12 is an exhaust-tube support, 13 is an interaction space, 14 and 15 are inner and outer straps, respectively, 16 and 17 are upper and lower cap-shaped sealing metals, respectively, 18 is a metal gasket, and 19 is an output section. The output section 19 includes the antenna lead 7, the antenna 8, the exhaust tube 9 and the antenna cover 10. Reference numeral 20 denotes a magnetic circuit section which includes the permanent magnets 4, 4a serving as sources of magnetic fields, the shallow-dish-shaped pole pieces 5, 5a, and the yokes 6, 6a. 
Reference numeral 21 denotes an upper end shield, 22 is a lower end shield, 23 and 24 are cathode leads (23 is a center lead and 24 is a side lead), 25 is an input-side ceramic, 26 arecathode terminals, 27 are lead-in wires, and 28 is a cathode section. The cathode section 28 includes the cathode filament serving as a thermionic electron source, the upper and lower end shields 21, 22, and the cathode leads 23, 24.
Reference numeral 29 denotes an anode section, which includes the plural anode vanes 2, the anode cylinder 3, and the inner and outer straps 14, 15. Reference numeral 31 denote choke coils, 32 is a feed-through capacitor, 33 is a filter case, 34 is a lid, and 45 are cooling fins.
In FIG. 16, the plural anode vanes 2 are fixed to the anode cylinder 3 as by brazing, or are fabricated integrally with the anode cylinder 3 by press working, such that the plural anode vanes 2 surround the helical cathode filament 1.
The pole pieces 5, 5a made of ferromagnetic material such as soft iron and the annular permanent magnets 4, 4a are disposed above and below the anode cylinder 3.
Magnetic fluxes from the permanent magnets 4, 4a enter the interaction space 13 defined between the cathode filament 1 and the anode vanes 2 through the pole pieces 5, 5a, and thereby provide a required axial DC magnetic field.
The yokes 6, 6a form part of amagnetic circuit for passing the magnetic fluxes from the permanent magnets 4, 4a. The magnetic circuit comprises the yokes 6, 6a, the permanent magnets 4, 4a, and the pole pieces 5, 5a. 
Electrons emitted from the cathode filament 1 at a negative high potential rotate about the cathode filament axis acted upon simultaneously an electric field and a magnetic field, and thereby generate a microwave electric field at each of the anode vanes 2. The generated microwave electric fields reach the antenna 8 via the antenna lead 7, and are output to an external device from the antenna cover 10.
The cathode filament 1 is generally made of a tungsten wire containing about 1% of thorium oxide (ThO2) in view of electron emission characteristics and workability, and is supported by the upper end shield 21, the lower end shield 22, and the cathode leads 23, 24.
The cathode leads 23, 24 are generally made of molybdenum (Mo) in view of heat resistance and workability, and are connected to the lead-in wires 27, 27 via terminal plates 26 brazed on the top of the input side ceramic 25 as by silver solder. The lead-in wires 27, 27 are connected to the choke coils 31, 31.
Attached to the underside of the magnetron is a filter structure comprising the filter case 33 housing the choke coils 31 and the feed-through capacitor 32 and the lid 34 for closing the opening of the filter case 33.
The choke coils 31 connected to the lead-in wires 27 form an L-C filter with the feed-through capacitor 32 and suppress low frequency components propagating through the cathode leads 23, 24. Microwave components are shielded by the filter case 33 and the lid 34.
The cooling fins 35 fitted around the anode cylinder 3 radiate heat generated by operation of the magnetron.
FIG. 17 is a schematic cross-sectional view of an essential part of a microwave oven serving as an example of conventional processing equipment of the coaxial waveguide type using a magnetron as a microwave generator. In FIG. 17, reference numeral 41 denotes a cooking chamber of the microwave oven, and material 43 to be heated is placed in the cooking chamber via a door 42. Reference numeral 44 denotes the magnetron, and 45 is a heating antenna, which is connected to the magnetron 44 via the coaxial waveguide 46. Microwaves generated by the magnetron 44 are supplied to the cooking chamber 41 in which the material 43 to be heated is placed, via the coaxial waveguide 46, and heat the material 43 by irradiating the material 43.
The coaxial waveguide 46 comprises a cylindrical outer conductor 47 and an inner conductor 48 placed concentrically with the outer conductor 47.
Further, for a magnetron of the type having the antenna 8 of the structure in which the antenna lead 7 is sandwiched hermetically between the exhaust tube 9 as shown in FIG. 16, a structure is proposed in Japanese Patent Application Laid-open No. Hei 7-282737, for example, in which the inner conductor 48 of the coaxial waveguide 46 is connected to the antenna cover 10, and the outer conductor 47 is fixed to the yoke 6a. 
Further, as another example of the conventional structure for coupling the magnetron to the waveguide, a structure employing a waveguide having no inner conductor is also proposed for processing equipment such as semiconductor device manufacturing equipment, as well as the heat processing equipment such as the microwave oven. In the processing equipment employing the waveguide having no inner conductor, microwaves are supplied to a processing chamber by projecting the antenna into the waveguide, unlike in the above-described case employing the coaxial waveguide.
The other references disclosing the structures of such magnetrons and processing equipment are Japanese Utility Model Application Laid-open Nos. Sho 53-9541, Sho 53-9542, Japanese Patent Application Laid-open Nos. Hei 2-79331, Hei 9-74083, Hei 9-82688, and Hei 9-82691, for example.
It is an object of the present invention to provide a small-sized, lightweight, high-power output magnetron, processing equipment employing this magnetron, and a coupling structure between the magnetron and a coaxial waveguide.
To achieve the above objects, in accordance with an embodiment of the present invention, there is provided a magnetron comprising: an anode cylinder; a plurality of vanes extending radially inwardly from the anode cylinder; a cathode filament extending along a center axis of the anode cylinder; an output section including an antenna coupled to one of the plurality of vanes; and a magnetic circuit section for supplying a magnetic field into the anode cylinder, whereby the magnetron oscillates at a fundamental frequency in a range from 400 MHz to 600 MHz.
To achieve the above objects, in accordance with another embodiment of the present invention, there is provided a magnetron comprising: an anode cylinder; a plurality of vanes extending radially inwardly from the anode cylinder; a cathode filament extending along a center axis of the anode cylinder; an output section including an antenna coupled to one of the plurality of vanes; and a magnetic circuit section for supplying a magnetic field into the anode cylinder, whereby the output section is provided with a cup-shaped antenna cover forming a part of the antenna, and is adapted to be coupled with a coaxial waveguide by connecting the coaxial waveguide to a conductive antenna block fixed to a bottom of the cup-shaped antenna cover.
To achieve the above objects, in accordance with another embodiment of the present invention, there is provided processing.equipment comprising: a magnetron comprising an anode cylinder, a plurality of vanes extending radially inwardly from the anode cylinder, a cathode filament extending along a center axis of the anode cylinder, an output section including an antenna coupled to one of the plurality of vanes, and a magnetic circuit section for supplying a magnetic field into the anode cylinder, the magnetron oscillating at a fundamental frequency in a range from 400 MHz to 600 MHz; and a processing section for processing a substance to be processed by using microwaves supplied from the magnetron, wherein the output section provides the microwaves to the processing section via a coaxial waveguide.
To achieve the above objects, in accordance with an embodiment of the present invention, there is provided a magnetron comprising: an anode cylinder; a plurality of vanes extending radially inwardly from the anode cylinder; a cathode filament extending along a center axis of the anode cylinder; an output section including an antenna coupled to one of the plurality of vanes; and a magnetic circuit section for supplying a magnetic field into the anode cylinder, the magnetron oscillating at a fundamental frequency in a range from 400 MHz to 600 MHz, wherein a ratio F/G of an outside diameter F of the cathode filament to a diameter G of a circle tangent to tips of the plurality of vanes satisfies one of the following inequalities: 0.44xe2x89xa6F/Gxe2x89xa60.54, when N=8, 0.52xe2x89xa6F/Gxe2x89xa60.64, when N=10, 0.59xe2x89xa6F/Gxe2x89xa60.73, when N=12, and 0.63xe2x89xa6F/Gxe2x89xa60.77, when N=14, where N is the number of the plurality of vanes.
The present invention is not limited to the above structures or the structures of the embodiments described subsequently, and various changes and modifications may be made without departing from the scope of the invention as defined in the appended claims.